Radio terminal device, transmission directivity control method, and transmission directivity control program

ABSTRACT

An adaptive array terminal ( 2000 ) includes a reception adaptive array unit ( 2030 ) extracting a reception signal from a base station by multiplying signals from respective antennas (#AN  1 –#AN  2 ) of an array antenna by respective reception weights, a transmission adaptive array unit ( 2090 ) applying to respective antennas of the array antenna a plurality of signals generated by multiplying by a transmission signal by transmission weights to form transmission directivity, and a transmission weight calculator ( 2070 ) calculating transmission weights added with a specified constraint in accordance with designation in a reception signal.

TECHNICAL FIELD

The present invention relates to the configuration of a radio terminalapparatus employed in radio communication of a mobile phone and thelike, a transmission directivity control method of such a radio terminalapparatus, and a transmission directivity control program.

BACKGROUND ART

In the field of mobile communication system (for example, personalhandyphone system: hereinafter PHS) evolving rapidly this few years, aPDMA (Path Division Multiple Access) system that allows mobile terminalapparatuses of a plurality of users to effect path multiple connectionto a radio base system by dividing the same time slot of the samefrequency spatially has been proposed in order to improve the usageefficiency of radio frequency. In the PDMA system, the signals from themobile terminal apparatuses of respective users are separated andextracted by the well-known adaptive array processing. The PDMA systemis also called the SDMA system (Spatial Division Multiple Access).

FIG. 18 represents the channel arrangement of the various communicationsystems of frequency division multiple access (FDMA), time divisionmultiple access (TDMA), and spatial division multiple access (SDMA).

First, FDMA, TDMA and SDMA will be described briefly with reference toFIG. 18. FIG. 18( a) corresponds to FDMA. The analog signals of users1–4 are subjected to frequency-division and transmitted over radio wavesof different frequencies f1–f4. The signals of respective users 1–4 areseparated by frequency filters.

FIG. 18( b) corresponds to TDMA. Digitized signals of respective usersare transmitted over radio waves at different frequencies f1–f4, andtime-divided on the basis of the prescribed period of time (time slot).The signals of respective users are separated by means of frequencyfilters and time-synchronization between a base station and mobileterminal devices of respective users.

The SDMA system has now been proposed to improve the usage efficiency ofradio frequency in accordance with the spread of mobile phones. The SDMAsystem spatially divides one time slot of the same frequency to transmitdata of a plurality of users, as shown in FIG. 18( c). In this SDMA, thesignals of respective users are separated by means of frequency filters,time synchronization between a base station and mobile terminal devicesof respective users, and a mutual interference canceller such as anadaptive array.

The adaptive array processing set forth above is well known in the fieldof art, and is described in detail in, for example, “Adaptive SignalProcessing by Array Antenna” (Kagaku Gijutsu Shuppan), issued Nov. 25,1998, pp. 35–49, “Chapter 3: MMSE Adaptive Array” by Nobuyoshi Kikuma.The conventional adaptive array processing will be described brieflyhereinafter.

FIG. 19 is a schematic block diagram of a configuration of atransmission and reception system 5000 of a conventional base stationfor SDMA.

In the configuration shown in FIG. 19, four antennas #1–#4 are providedto establish identification between users PS1 and PS2. In a receptionoperation, the outputs of antennas are provided to an RF circuit 5101 tobe amplified by the reception amplifier, and then frequency-converted bya local oscillation signal. The converted signals have the unnecessaryfrequency signal removed by filters, then subjected to A/D conversion,and applied to a digital signal processor 5102 as digital signals.

Digital signal processor 5102 includes a channel allocation referencecalculator 5103, a channel allocating apparatus 5104, and an adaptivearray 5100. Channel allocation reference calculator 5103 calculates inadvance whether the signals from the two users can be separated by theadaptive array. Based on the calculation result, channel allocationapparatus 5104 provides channel allocation information including userinformation, selecting frequency and time, to adaptive array 5100.Adaptive array 5100 applies a weighting operation in real time on thesignals from the four antennas #1–#4 based on the channel allocationinformation to separate only the signals of a particular user.

[Configuration of Adaptive Array Antenna]

FIG. 20 is a block diagram showing a configuration of a transmission andreception unit 5100 a corresponding to one user in adaptive array 5100.The example of FIG. 20 has n input ports 5020-1 to 5020-n to extract thesignal of the desired user from input signals of a plurality of users.

The signals input to respective input ports 5020-1 to 5020-n are appliedvia switch circuits 5010-1 to 5010-n to a weight vector control unit5011 and multipliers 5012-1 to 5012-n.

Weight vector control unit 5011 calculates weight vectors w_(1i)–w_(ni)using input signals, a unique word signal corresponding to signals of aparticular user prestored in a memory 5014, and the output from an adder5013. In the present specification, subscript “i” implies that theweight vector is employed for transmission/reception with the i-th user.

Multipliers 5012-1 to 5012-n multiply the input signals from input ports5020-1 to 5020-n by weight vectors w_(1i)–w_(ni), respectively. Themultiplied results are applied to adder 5013. Adder 5013 adds the outputsignals from multipliers 5012-1 to 5012-n to output the added signals asa reception signal S_(RX)(t). This reception signal S_(RX)(t) is alsoprovided to weight vector control unit 5011.

Transmission and reception unit 5100 a further includes multipliers5015-1 to 5015-n receiving and multiplying an output signal S_(TX)(t)from an adaptive array radio base station by respective weight vectorsw_(1i)–w_(ni) applied from weight vector control unit 5011. The outputsof multipliers 5015-1 to 5015-n are provided to switch circuits 5010-1to 5010-n, respectively. Specifically, switch circuits 5010-1 to 5010-nprovide the signals applied from input ports 5020-1 to 5020-n to asignal receiver unit 1R in a signal receiving mode, and provide thesignal from a signal transmitter unit 1T to input/output ports 5020-1 to5020-n.

[Operating Mechanism of Adaptive Array]

The operating mechanism of transmission and reception unit 5100 a ofFIG. 20 will be described briefly here.

For the sake of simplifying the description, it is assumed that thereare four antenna elements, and that two users PS effect communication atthe same time. Here, the signals applied to reception unit 1R fromrespective antennas are represented by the equations set forth below.RX ₁(t)=h ₁₁ Srx ₁(t)+h ₁₂ Srx ₂(t)+n ₁(t)  (1)RX ₂(t)=h ₂₁ Srx ₁(t)+h ₂₂ Srx ₂(t)+n ₂(t)  (2)RX ₃(t)=h ₃₁ Srx ₁(t)+h ₃₂ Srx ₂(t)+n ₃(t)  (3)RX ₄(t)=h ₄₁ Srx ₁(t)+h ₄₂ Srx ₂(t)+n ₄(t)  (4)

Signal RX_(j) (t) represents a reception signal of the j-th (j=1, 2, 3,4) antenna. Signal Srx_(i) (t) represents a signal transmitted by thei-th (i=1, 2) user. Coefficient h_(ji) represents the complexcoefficient of a signal from the i-th user received at the j-th antenna,and n_(j) (t) represents noise included in the j-th reception signal.

The above equations (1)–(4) may be represented in vector form asfollows:X(t)=H ₁ Srx ₁(t)+H ₂ Srx ₂(t)+N(t)  (5)X(t)=[RX ₁(t), RX ₂(t), . . . , RX _(n)(t)]^(T)  (6)H _(i) =[h _(1i) , h _(2i) , . . . , h _(ni)]^(T), (i=1, 2)  (7)N(t)=[n ₁(t), n ₂(t), . . . , n _(n)(t)]^(T)  (8)

In equations (6)–(8), [. . . ]^(T) denotes the transposition of [. . .]. Here, X (t) represents the input signal vector, H_(i) the receptionsignal coefficient vector of the i-th user, and N (t) a noise vector.

The adaptive array antenna outputs as a reception signal S_(RX)(t) asynthesized signal obtained by multiplying the input signals fromrespective antennas by respective weight coefficients w_(1i)–w_(ni), asshown in FIG. 20. Here, The number of antennas n is 4.

Given these preliminaries, the operation of an adaptive array in thecase of extracting a signal Srx₁ (t) transmitted by the first user, forexample, is set forth below.

Output signal y1 (t) of adaptive array 2100 can be represented by thefollowing equations by multiplying input signal vector X(t) by weightvector W₁.y1(t)=X(t) W ₁ ^(T)  (9)W_(1 =[w) _(11, w) _(21, w) _(31 , w) ₄₁]^(T)  (10)

In other words, weight vector W₁ is a vector with the weightcoefficients w_(j1)(=1, 2, 3, 4) to be multiplied by the j-th inputsignal RXj (t) as elements.

Substituting input signal vector X (t) represented by equation (5) intoy1 (t) represented by equation (9) yields:y1(t)=H ₁ W ₁ ^(T) Srx ₁(t)+H ₂ W ₁ ^(T) Srx ₂(t)+N(t)W ₁ ^(T)  (11)

By a well known method, weight vector w₁ is sequentially controlled byweight vector control unit 5011 so as to satisfy the followingsimultaneous equations when adaptive array 5100 operates in an idealsituation.H₁W₁ ^(T)=1  (12)H₂W₁ ^(T)=0  (13)

If weight vector W₁ is perfectly controlled so as to satisfy equations(12) and (13), output signal y1 (t) from adaptive array 2100 iseventually represented by the following equations.y1(t)=Srx ₁(t)+N ₁(t)  (14)N ₁(t)=n ₁(t)w ₁₁ +n ₂(t)w ₂₁ +n ₃(t)w ₃₁ +n ₄(t)w ₄₁  (15)

Specifically, signal Srx₁ (t) transmitted from the first of the twousers will be obtained for output signal y1 (t).

In FIG. 20, input signal S_(TX) (t) for adaptive array 5100 is appliedto transmitter unit 1T in adaptive array 2100 to be applied torespective one inputs of multipliers 5015-1, 5015-2, 5015-3, . . . ,5015-n. To the other inputs of these multipliers, weight vectors w_(1i),w_(2i), w_(3i), . . . , w_(ni) calculated by weight vector control unit5011 based on reception signals described above are copied and applied.

The input signals weighted by these multipliers are delivered tocorresponding antennas #1, #2, #3, . . . , #n via corresponding switches5010-1, 5010-2, 5010-3, 5010-n for transmission.

FIG. 21 is a schematic diagram to describe a configuration of signalstransferred between a terminal and SDMA base station 5000.

The signals of 1 frame are divided into 8 slots, the 4 slots of theformer half directed to, for example, reception, and the 4 slots of thelatter half directed to, for example, transmission.

Each slot is formed of 120 symbols. Based on one slot for reception andone slot for transmission as one set, the signals of 1 frame can beallocated to as many as 4 users in the example of FIG. 21.

Identification of users PS1 and PS2 is established as set forth below. Aradio wave signal of a mobile phone is transmitted taking a frame formset forth above. The slot signal from a mobile phone is mainly composedof a preamble formed of a signal series known to a radio base station,and data (voice and the like) formed of a signal series unknown to theradio base station.

The preamble signal series includes a signal stream of information toidentify whether the current user is the appropriate user to conversefor the radio base station. Weight vector control unit 5011 of adaptivearray radio base station 1 compares the unique word signal output frommemory 5014 with the received signal series to conduct weight vectorcontrol (determination of weight coefficient) so as to extract thesignal expected to include the signal series corresponding to user PS1.

It is assumed that each frame includes the above-described unique wordsignal (reference signal) zone, and takes a configuration that allowserror detection by a cyclic code (CRC: cyclic redundancy check).

In addition to the case where adaptive array processing is carried outat the base station to establish transmission or reception directivity,there are cases where adaptive array processing is carried out at thereception terminal side. A terminal that carries out adaptive arrayprocessing in such terminals (mobile station) is referred to as an“adaptive array terminal”.

Such an adaptive array terminal always carries out an adaptive arrayoperation in both the reception mode and transmission mode. Therefore,the response vector of a signal from the terminal, when connected to theabove-described SDMA base station, will vary for each frame, posing theproblem that the communication quality may be degraded in multipleaccess.

This problem will be described in further detail hereinafter.

FIG. 22 schematically shows a state where radio communication isconducted between an adaptive array base station CS1 and respectiveterminals of an adaptive array terminal PS1 and a terminal PS2 thatcarries out the general non-directional transmission and reception.

Referring to FIG. 22, a plurality of the same signals arrive at SDMAbase station CS1 by multipath propagation from adaptive array terminalPS1. The reception signal response vector of a signal from adaptivearray terminal PS1 is represented as in the equations set forth below asa composite vector of a plurality of signals.X(t)=H ₁₁ W ₁ S ₁(t)+. . . +H _(1m) W ₂ S ₁(t)+H ₂ S ₂(t)  (16)X(t)=H ₁ S ₁(t)+H ₂ S ₂(t)  (17)H ₁ =H ₁₁ W ₁ +. . . +H _(1m) W ₂  (18)

At SDMA base station CS1, the reception signal response vector(composite vector) for the signal from adaptive array terminal PS1depends on the weights (W₁, W₂) of the transmission adaptive arrayprocessing of adaptive array terminal PS1.

This means that, when the weights of the transmission weight change atthe adaptive array terminal PS1, the reception signal response vectorwill be altered at SDMA base station CS1 even if there is absolutely novariation in the propagation path itself.

In other words, the transmission weights may suddenly be shiftedindependent of variation in propagation due to terminal noise,calculation error, and the like.

When spatial multiplexing is to be carried out, SDMA base station CS1measures the reception response vector for each of the multipleterminals. Multiple access communication (SDMA system communication) isallowed when the spatial correlation between the reception responsevectors of the multiple terminals is equal to or below a thresholdvalue.

Therefore, when adaptive array transmission is effected on the part ofterminal PS1, there may be a case where the reception signal responsevector viewed from the SDMA base station CS1 side varies suddenly andunpredictably, imposing the problem that the multiplex communicationwill be degraded in quality.

FIG. 23 shows a reception signal response vector H₁ as a compositevector with respect to signals propagated via a plurality of paths fromadaptive array terminal PS1.

Since such a reception signal response vector is altered depending onvariation in the propagation path as described above as well as by othervarious factors, the reception signal response vector H₁ applied as acomposite vector may be altered more greatly than the variation in thepropagation path.

The present invention is directed to solve the above-described problems.An object is to provide a radio terminal apparatus that conductsadaptive array processing, allowing radio communication with an SDMAbase station while maintaining favorable communication quality, atransmission directivity control method and a transmission directivitycontrol program thereof.

DISCLOSURE OF THE INVENTION

In summary, the present invention includes an array antenna having aplurality of antennas, a reception signal processing unit extracting areception signal from a base station by multiplying signals fromrespective antennas of the array antenna by respective receptionweights, a transmission signal processing unit applying to respectiveantennas of the array antenna a plurality of signals generated bymultiplying a transmission signal by transmission weights to formtransmission directivity, and transmission weight generation means foradaptively switching between a mode of calculating transmission weightsforming transmission directivity towards the base station and a mode ofcalculating transmission weights added with a specified constraint, inaccordance with designation in the reception signals to generatetransmission weights.

Preferably, when the reception signal processing unit multiplies asignal from the base station by reception weights having receptiondirectivity, the transmission weight generation means provides thereception weights to the transmission signal processing unit as thetransmission weights, in accordance with designation from the basestation.

Preferably, when the reception signal processing unit multiplies asignal from the base station by reception weights having receptiondirectivity, the transmission weight generation means generates thetransmission weights based on a transmission response vector estimatedfrom a reception response vector, in accordance with designation fromthe base station.

Preferably, when the reception signal processing unit multiplies asignal from the base station by reception weights having receptiondirectivity, the transmission weight generation means sets thetransmission weight with a fixed amplitude and phase, in accordance withdesignation from the base station.

Preferably, when the reception signal processing unit multiplies asignal from the base station by reception weights having receptiondirectivity, the transmission weight generation means carries out aprocess of setting a fixed value of amplitude of the transmissionweight, and gradually shifting a phase of the transmission weightaccording to a predetermined sequence, in accordance with designationfrom the base station.

Further preferably, a signal transferred between the base station and aradio terminal apparatus is divided into a plurality of frames, and thetransmission weight generation means calculates the phase of thetransmission by a weighted mean of the reception weights in past andcurrent frames.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. When thereception signal processing unit multiplies a signal from the basestation by reception weights having reception directivity, thetransmission weight generation means calculates the transmission weightbased on a weighted mean of reception response vectors in past andcurrent frames, in accordance with designation from the base station.

Preferably, the radio terminal apparatus further includes receptionlevel detection means for detecting a reception level of each of theantennas. The transmission weight generation means generates thetransmission weights so as to select an antenna of the highest receptionlevel.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. When thereception signal processing unit multiplies a signal from the basestation by reception weights having reception directivity, thetransmission weight generation means newly takes a weighted mean oftransmission weights calculated in the past and current frames as atransmission weight of the current frame, in accordance with designationfrom the base station.

Preferably, the radio terminal apparatus further includes storage meansfor storing in advance a set of transmission weights that increasesorthogonality of reception response vectors at the base station. Thetransmission weight generation means selects and provides to thetransmission signal processing unit the transmission weight stored inthe storage means, in accordance with designation from the base station.

According to another aspect of the present invention, a transmissiondirectivity control method of a radio terminal apparatus including anarray antenna having a plurality of antennas and for separating andextracting a reception signal from a base station by multiplying signalsfrom respective antennas of the array antenna by respective receptionweights, includes the steps of: adaptively switching between a mode ofcalculating transmission weights forming transmission directivitytowards the base station and a mode of calculating the transmissionweights added with a specified constraint, in accordance withdesignation in a reception signal, to generate the transmission weightsand providing to respective antennas of the array antenna a plurality ofsignals generated by multiplying a transmission signal by thetransmission weights to form the transmission directivity.

Preferably, the step of generating transmission weights includes thestep of taking the reception weights as the transmission weights when asignal from the base station is multiplied by reception weights havingreception directivity, in accordance with designation from the basestation.

Preferably, the step of generating transmission weights includes thestep of generating the transmission weights based on a transmissionresponse vector estimated from a reception response vector a signal fromthe base station is multiplied by reception weights having receptiondirectivity, in accordance with designation from the base station.

Further preferably, the step of generating transmission weights includesthe step of setting the transmission weight with a fixed amplitude andphase when a signal from the base station is multiplied by receptionweights having reception directivity, in accordance with designationfrom the base station.

Preferably, the step of generating transmission weights includes thestep of carrying out a process of setting a fixed value of amplitude ofthe transmission weight, and gradually shifting a phase of thetransmission weight according to a predetermined sequence when thereception signal processing unit multiplies a signal from the basestation by reception weights having reception directivity, in accordancewith designation from the base station.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of calculating a phaseof the transmission weight based on a weighted mean of reception weightsin past and current frames.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of calculating thetransmission weight based on a weighted mean of reception responsevectors in past and current frames when a signal from the base stationis multiplied by reception weights having reception directivity, inaccordance with designation from the base station.

Preferably, the method further includes the step of detecting areception level of each of the antennas. The step of generatingtransmission weights includes the step of generating the transmissionweights so as to select an antenna of highest reception level.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of newly taking aweighted mean of transmission weights calculated in the past and currentframes as a transmission weight of the current frame when a signal fromthe base station is multiplied by reception weights having receptiondirectivity in accordance with designation from the base station.

Preferably, the method further includes the step of storing in advance aset of transmission weights that increases the orthogonality of areception response vector at the base station. The step of generatingtransmission weights includes the step of selecting the transmissionweight stored in advance in accordance with designation from the basestation.

According to a further aspect of the present invention, a transmissiondirectivity control program of a radio terminal apparatus including anarray antenna having a plurality of antennas and for separating andextracting a reception signal from a base station by multiplying signalsfrom respective antennas of the array antenna by respective receptionweights, causes a computer to execute the steps of: adaptively switchingbetween a mode of calculating transmission weights forming transmissiondirectivity towards the base station and a mode of calculating thetransmission weights added with a specified constraint, in accordancewith designation in the reception signal to generate transmissionweights and providing to respective antennas of the adaptive array aplurality of signals generated by multiplying a transmission signal bytransmission weights to form the transmission directivity.

Preferably, the step of generating transmission weights includes thestep of taking the reception weights as the transmission weights when asignal from the base station is multiplied by reception weights havingreception directivity, in accordance with designation from the basestation.

Preferably, the step of generating transmission weights includes thestep of generating the transmission weights based on a transmissionresponse vector estimated from a reception response vector when a signalfrom the base station is multiplied by reception weights havingreception directivity, in accordance with designation from the basestation.

Preferably, the step of generating transmission weights includes thestep of setting the transmission weight with a fixed amplitude and phasewhen a signal from the base station is multiplied by reception weightshaving reception directivity, in accordance with designation from thebase station.

Preferably, the step of generating transmission weights includes thestep of carrying out a process of setting a fixed value of amplitude ofthe transmission weight, and gradually shifting a phase of thetransmission weight according to a predetermined sequence when a signalfrom the base station is multiplied by reception weights havingreception directivity, in accordance with designation from the basestation.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of calculating a phaseof a transmission weight based on a weighted mean of reception weightsin past and current frames.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of calculating thetransmission weights based on a weighted mean of reception responsevectors in past and current frames when a signal from the base stationis multiplied by reception weights having reception directivity inaccordance with designation from the base station.

Preferably, the method further includes the step of detecting areception level of each of the antenna. The step of generatingtransmission weights includes the step of generating transmissionweights so as to select an antenna of highest reception level.

Preferably, a signal transferred between the base station and a radioterminal apparatus is divided into a plurality of frames. The step ofgenerating transmission weights includes the step of newly taking aweighted mean of transmission weights calculated in the past and currentframes as the transmission weight of the current frame when a signalfrom the base station is multiplied by reception weights havingreception directivity, in accordance with designation from the basestation.

Preferably, the program further includes the step of storing in advancea set of transmission weights that increases the orthogonality of areception response vector at the base station. The step of generatingtransmission weights includes the step of selecting the transmissionweight stored in advance in accordance with designation from the basestation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a configuration of an SDMAbase station 1000 according to a first embodiment of the presentinvention.

FIG. 2 is a schematic block diagram to describe a configuration of anadaptive array terminal 2000 of the present invention.

FIG. 3 is a flow chart to describe an operation of adaptive arrayterminal 2000.

FIG. 4 represents a process flow when base station 1000 transmits asignal having directivity to adaptive array terminal 2000.

FIG. 5 is a flow chart to describe a first transmission and receptionflow when base station 1000 is an SDMA base station.

FIG. 6 is a flow chart exemplifying a second operation when base station1000 is an SDMA base station.

FIG. 7 is a flow chart exemplifying a third operation when base station1000 is an SDMA base station.

FIG. 8 is a flow chart to describe an operation when a terminal 2200 hastransmission weight select capability and a base station 1002 is an SDMAbase station.

FIG. 9 is a schematic block diagram to describe a configuration of anSDMA base station 1002.

FIG. 10 is a schematic block diagram to describe a configuration of anadaptive array terminal 2200 having transmission weight selectcapability.

FIG. 11 is a first flow chart to describe a processing flow of tableproduction with respect to a memory 2220.

FIG. 12 is a second flow chart to describe a processing flow of tableproduction with respect to memory 2220.

FIG. 13 is a flow chart to describe a method of communication between aterminal and a base station with a transmission weight selected.

FIG. 14 is a schematic diagram showing a state of a plurality ofarriving signals at an SDMA base station CS1.

FIG. 15 is a schematic diagram to describe a reception response vectorH₁ when a plurality of arriving signals are represented as a compositevector.

FIG. 16 is a schematic diagram to describe a reception response vectorof a signal from adaptive array terminal PS1 over time.

FIG. 17 is a schematic diagram to describe a reception response vectorsubsequent to designation of altering the transmission weight.

FIG. 18 shows channel arrangement in respective communication systems offrequency division multiple access, time division multiple access, andspatial division multiple access.

FIG. 19 is a schematic block diagram of a configuration of atransmission and reception system 5000 of a conventional SDMA basestation.

FIG. 20 is a block diagram of a configuration of a transmission andreception unit 5100 a corresponding to one user in an adaptive array5100.

FIG. 21 is a schematic diagram to describe a configuration of a signaltransferred between a terminal and an SDMA base station 5000.

FIG. 22 is a schematic diagram showing a state where radio communicationis effected between adaptive array base station CS1 and respectiveterminals of an adaptive array terminal PS1 and a terminal PS2 thatcarries out general non-directional transmission and reception.

FIG. 23 shows a reception signal response vector H₁ as a compositevector with respect to signals propagated via a plurality of paths fromadaptive array terminal PS1.

BEST MODE TO CARRY OUT THE INVENTION

FIG. 1 is a schematic block diagram showing a structure of an SDMA basestation 1000 according to a first embodiment of the present invention.

Referring to FIG. 1, SDMA base station 1000 includes transmission andreception units TRP1–TRP4 applying transmission signals to an arrayantenna composed of a plurality of antennas #1–#4, or receivingreception signals, a signal processing unit USP1 receiving signals fromtransmission and reception units TRP1–TRP4 to carry out processing ofsignals corresponding to, for example, a user 1, a signal processingunit USP2 receiving signals from transmission and reception unitsTRP1–TRP4 to carry out signal processing of signals corresponding to auser 2, a modulation-demodulation unit MDP to modulate a signal to beapplied to signal processing units USP1 and USP2, or to demodulatesignals from signal processing units USP1 and USP2, a baseband unit BBPgenerating digital signals to be transmitted and received to and fromsignal processing units USP1 and USP2 via modulation-demodulation unitMDP, a control unit CNP controlling the operation of SDMA base station1000, and a terminal receiving antenna designation adding unit IAP toadd, in accordance with designation from control unit CNP, controlinformation to designate an antenna to be used at the user terminal, aswell as type information indicating the type of base station 1000, i.e.,whether base station 1000 is a base station that carries outnondirectional transmission and reception or an SDMA base station, withrespect to a transmission signal that is provided from baseband unit BBPto modulation-demodulation unit MDP.

Transmission and reception unit TRP1 includes a transmission unit TP1 tocarry out high frequency signal processing in a transmission mode, areception unit RP1 to carry out high frequency signal processing in areception mode, and a switch unit SW1 to switch the connection ofantenna #1 with respect to transmission unit TP1 or reception unit RP1depending on whether in a transmission mode or a reception mode. Theremaining transmission and reception units TR2–TR4 have a similarconfiguration.

The above description is based on the case where the number of antennasis 4 and there are 2 users. Generally, the number of antennas is N (n:natural number), and multiple users as many as those corresponding tothe degree of freedom based on the number of antennas are allowed.

Further, base station 1000 can also conduct non-directional transmissionby setting the transmission weight to zero except for a certain antennaunder control of control unit CNP. The same applies for reception,allowing non-directional reception. Although not particularly limited,the function of control unit CNP can be realized, based on a computerprogram, by a processor that sequentially executes the proceduredesignated by the program.

FIG. 2 is a schematic block diagram to describe a configuration of anadaptive array terminal 2000 of the present invention.

Referring to FIG. 2, adaptive array terminal 2000 includes an adaptivearray antenna composed of antennas #AN1 and #AN2 to carry out datatransmission and reception, a reception level measurement unit 2010measuring the reception levels of antennas #AN1 and #AN2, switch units2020 and 2022 applying a transmission signal to antennas #AN1 and #AN2,respectively, in a transmission mode, and passing through receptionsignals from the antenna in a reception mode, a reception adaptive arrayunit 2030 receiving and carrying out adaptive array processing onsignals from switch units 2020 and 2022 to separate a signal from adesired base station, and a demodulation circuit 2040 to carry out ademodulation process on a signal from reception adaptive array unit 2030to extract a baseband signal.

Adaptive array terminal 2000 further includes an error determinator 2050to determine the amount of error of the reception signal according tothe above-described CRC, based on an output from demodulation circuit2040, a base station type identify device 2060 to identify, based on anoutput from demodulation circuit 2040, whether the base station is abase station that carries out transmission and reception in accordancewith the SDMA system or a base station of another type, a transmissionweight calculator 2070 to calculate transmission weights based on thereception signal information from error determinator 2050 and basestation type identify device 2060 and the reception signal informationfrom reception adaptive array unit 2030, and a memory 2100 to retain inadvance phase information and the like for control of transmissiondirectivity, as will be described afterwards.

As used herein, “reception signal information” implies information thatcharacterizes the signal received at the base station such as theabove-described reception level and reception error, control informationfrom the base station, a reception response vector, and the like. In thepresent invention, the control method of transmission directivity ismodified conforming to “reception signal information” at a terminal 2000capable of adaptive array control in both transmission and receptionmodes, as will be described afterwards.

Adaptive array terminal 2000 further includes a modulation circuit 2080receiving a transmitted baseband signal to carry out a modulationprocess, and a transmission adaptive array unit 2090 receiving an outputfrom modulation circuit 2080 and transmission weights from transmissionweight calculator 2070 to carry out transmission adaptive arrayprocessing.

As will become apparent by the description set forth below, adaptivearray terminal 2000 is at least characterized in that sudden change ofthe transmission weight to cause degradation in communication quality issuppressed by transition from an operation mode in which the receptionweight and transmission weight are adaptively altered to an operationmode that adds a predetermined constraint on the reception weight andtransmission weight in accordance with “reception signal information”,in response to designation from base station 1000.

Although not particularly limited, the function of adaptive arrayterminal 2000 can be realized, based on a computer program, by aprocessor not shown directed to sequentially execute the proceduredesignated by the program, controlling the operation of respectivestructural elements of adaptive array terminal 2000.

The operation of transmission weight calculator 2070, among theconfiguration of adaptive array terminal 2000, will be described infurther detail hereinafter.

It is assumed that transmission weight calculator 2070 conductstransmission and reception selectively using a transmission directivitycontrol method that will be described hereinafter, based on theabove-described “reception signal information”. As used herein, eachoperating mode based on designation of “a transmission directivitycontrol method” is called a “transmission mode”. Further, “a receptiondirectivity control method” in the reception mode can be selectivelymodified at adaptive array terminal 2000. Respective modes that operateunder the specified reception directivity control method is called a“reception mode”.

(1. When Copying Reception Weight as Transmission Weight)

When reception weights are to be copied, transmission weight calculator2070 receives reception weights from reception adaptive array unit 2030,and transfers the same as the transmission weights. If the communicationstatus is favorable, communication having the interference with respectto another terminal removed can be effected by establishing directivityin transmission and reception also at the terminal side.

(2. When Calculating Transmission Weight Based on Reception ResponseVector)

Transmission weight calculator 2070 can estimate a reception responsevector for a transmission mode based on a reception response vector of asignal from a terminal in the reception mode, and conduct calculation oftransmission weights based on the estimated reception response vector inaccordance with the specified operation mode. This is advantageous inthat, if the communication status is favorable, optimum communicationdirectivity can be realized of a higher level as compared to the casewhere reception weights are simply copied and used as the transmissionweights.

A method of obtaining transmission weights based on such an estimatedvalue of a reception response vector will be described brieflyhereinafter. The reception response vectors at the uplink line slot aresequentially obtained, which are extrapolated by a predeterminedfunction (for example, linear function) until the time of transmissionto estimate the reception response vector for transmission.

Upon obtaining an estimated value of a reception response vector at thetransmission time point as described above, a transmission weight vectorcan be obtained by any of the three following methods.

2-i) Method by Orthogonalization

A weight vector W(1) (i)=[wtx₁₁, wtx₁₂, wtx₁₃, wtx₁₄] at time t=iT (i:natural number, T: unit time interval) of user PS1 will be considered.In order to direct null to user PS2, the conditions set forth below areto be satisfied.

It is assumed that the propagation path (reception response vector)predicted for user PS2 is V(2)(i)=[h1′(2)(i), h2′(2)(i), h3′(2)(i),h4′(2)(i)]. Here, hp′(q) (i) is a predicted value of the receptioncoefficient vector for the p-th antenna for the q-th user with respectto time i. Similarly, it is assumed that propagation path V(1) (i) ispredicted for user PS1.

Here, W(1) (i) is determined such that a relation ofW(1)(i)^(T)V(2)(i)=0 is established. As constraints, the followingconditions of c1) and c2) are imposed.

c1) W(1)(i)^(T)V(1)(i)=g (a constant value)

c2) ∥W⁽¹⁾(i)∥ is minimized.

Condition c2) is comparable to minimizing the transmission power.

2-ii) Method Using Spurious Correlation Matrix

Here, the adaptive array consists of some antenna elements, and aportion controlling each element weight value, as set forth above.Generally, when the input vector of the antenna is represented as X(t)and the weight vector is represented as W, an optimal weight W_(opt)will be given in the following equation (Wiener solution), if the weightvector is controlled so as to minimize the mean square error between anoutput Y(t)=W^(T)X(t) and a reference signal d(t) (MMSE standard:minimum mean square error standard).W_(opt)=R_(xx) ⁻¹r_(xd)  (19)

Here, the following equations have to be satisfied.R _(xx) =E[x*(t)^(T)(t)]  (20)r _(xd) =E[x*(t)d(t)]  (21)

Here, Y^(T) represents the transposition of Y, Y* represents a complexregion of Y, and E[Y] represents the ensemble average. Using the weightvalue, the adaptive array generates an array pattern so as to suppressunnecessary interfering waves.

In the method using a spurious correlation matrix, the foregoingequation (21) is calculated with a spurious correlation matrix as setforth below.

That is, a weight vector W(k) (i) for user k is calculated with anestimated complex reception signal coefficient h′(k)n (i). When an arrayresponse vector for the k-th user is represented as V(k) (i), the weightvector can be obtained in the following manner.V ^((k))(i)=[h′ ₁ ^((k))(i),h ₂ ^((k))(i) . . . , h′ _(N)^((k))(i)]  (22)

Here, an autocorrelation matrix Rxx(i) of an assumed reception signal att=iT is expressed in the following equation, using V(k)(i).

$\begin{matrix}{{R_{xx}(i)} = {{\sum\limits_{k = 1}^{K}{{V^{{(k)}*}(i)}{V^{{(k)}T}(i)}}} + {NI}}} & (23)\end{matrix}$

Here, N is an assumed noise term added so that Rxx (i) is regular. Forexample, N=1.0×10⁻⁵ in the calculation in the present invention.

A correlation vector rxd(i) of the reception signal with the referencesignal is expressed in the following equation.r _(xd)(i)=V ^((k))*(i)  (24)

Therefore, the weight for the downlink at time t=iT can be obtained withequations (21), (25), and (26).

The inverse matrix of equation (25) can optimally be calculated for userk with a lemma of the inverse matrix. In the case for two users, inparticular, the weight can be calculated by the following simpleequations.W ⁽¹⁾(i)=(p ₂₂ +N)V ⁽¹⁾*(i)−p ₁₂ V ⁽²⁾*(i)  (25)W ⁽²⁾(i)=(p ₁₁ +N)V ⁽²⁾*(i)−P ₂₁ V ⁽¹⁾*(i)p _(ij) =V ^((i)) ^(H) (i)V ^((j))(i)  (26)

A method for calculating a weight vector when the autocorrelation matrixis given as described above is disclosed in, for example, the followingreferences: T. Ohgane, Y. Ogawa, and K. Itoh, Proc. VTC '97, vol. 2, pp.725–729, May, 1997; or, Tanaka, Ohgane, Ogawa, Itoh, Technical Report ofIEICE, vol. RCS98–117, pp. 103–108, October 1998.

2-iii) Method of Directing Beam to User PS1

When attention is paid only to directing a beam to user PS1, only thefollowing equation has to be satisfied.W(1)(i)=V(1)(i)*

By the above-described methods, transmission weights can be calculatedbased on the estimated reception response vector.

(3. When Transmitting with Amplitude and Phase of Transmission WeightFixed: Directivity Fixed Transmission)

Alternatively, transmission weight calculator 2070 carries out a processto fix the amplitude with equal gain, and also to fix the phase forcalculating and outputting transmission weights based on the phaseinformation stored in memory 2100.

(4. When Transmitting While Altering Phase with Fixed Amplitude ofTransmission Weight: Directivity Sub-Fixed Transmission)

In the case where a mode of fixing the amplitude at equal gain andgradually altering the phase in accordance with designation from thecontrol unit is specified, the reception information (reception weight,reception response vector) is subjected to weighted mean with the pastreception information to calculate and output transmission weights fromthe phase.

For example, the weighted mean between a past weight Wrx_old and thecurrent reception weight Wrx is defined by the following equation.Wrx=(1−α)Wrx_old/|Wrx_old|+αWrx/|Wrx|where 1<α<0, and α a predetermined value.

The phase is extracted from this weight Wrx, and a weight is generatedbased on that phase information.

(5. When Transmitting in Reception Level Select Transmission DiversityMode)

In the case where a mode of selecting an antenna of high reception levelis specified, transmission weight calculator 2070 sets the weight of theantenna number to be selected to 1, and the weights of the antennas ofother antenna numbers to 0 based on the measurement result from thereception level measurement unit.

(6.1 When Carrying Out 1-Antenna Fixed Transmission)

In the case where a mode of transmitting in a fixed manner through onlyone of the antennas is specified based on the designated transmissionmode, the weight of one selected antenna number is set to 1 inaccordance with designation from the base station, and the weights ofantennas of other antenna numbers is set to 0 by transmission weightcalculator 2070. Alternatively, the antenna to be selected when the1-antenna fixed transmission mode is specified may be determined inadvance. In this case, the base station only has to instruct terminal2000 of designation of the 1-antenna fixed transmission mode.

(7. When Carrying Out Maximum Ratio Composite Transmission)

In the case where maximum ratio composite transmission is specified,transmission weight calculator 2070 sets the transmission weights suchthat the output signal intensity is maximum, irrespective of thedirectivity of the signal output from the antenna.

The above description is based on a transmission mode. Likewise in areception mode, the operation of various reception modes such as anadaptive array reception mode, maximum ratio composite reception,reception level select diversity, 1-antenna fixed reception and the likecan be realized by setting the values of the reception weights inaccordance with the designation.

Respective operation modes set forth above will be described in furtherdetail hereinafter

[Operation Example when Base Station is a Base Station that Carries OutNon-Directional Transmission]

The following description corresponds to an operation of adaptive arrayterminal 2000 when base station 1000 effects non-directionaltransmission, and space-multiplexed communication is not conducted. Inother words, an operation based on the case where the base station isnot an SDMA base station in accordance with the service area will bedescribed.

FIG. 3 is a flow chart to describe an operation of adaptive arrayterminal 2000 in such a case.

Referring to FIG. 3, terminal 2000 informs base station 1000 of areception allowable operation and transmission allowable operation (stepS100).

Informing a transmission allowable operation may be effected when, butnot particularly limited, degradation in the reception status isdetected by an error determinator 2050 at terminal 2000.

From the base station side, terminal 2000 is notified with controlinformation added to transmission information by terminal receptionantenna designation adding unit IAP such that any of the transmissionand reception modes set forth below is selected in accordance with theinformed contents from the terminal 2000 side (step S102).

For example, designation can be made so as to carry out adaptive arrayreception for reception and adaptive array transmission fortransmission.

Additionally in reception, designation can be made to carry out maximumratio composite reception so that the reception power is at the highestlevel, to carry out reception level select diversity reception so as toselect an antenna of higher reception level for reception at adaptivearray terminal 2000, or to carry out a 1-antenna fixed receptionoperation specifying that any one of the antennas is fixedly usedirrespective of the reception level.

For the transmission mode, a maximum ratio composition transmission modecan also be specified so as to output a transmission signal at thehighest transmission power. Alternatively, directivity fixedtransmission corresponding to transmission with the magnitude and phaseof the transmission weight fixed, or directivity sub-fixed transmissioncan be designated so as to have a predetermined directivity (directionof transmission).

Furthermore, a reception level select transmission diversity operationmode can be designated to select an antenna of higher reception levelfor transmission in accordance with the reception level. Alternatively,a 1-antenna fixed transmission mode using one of the antennas in a fixedmanner, independent of the reception level, can be specified.

At the terminal side, transmission is effected in accordance with theselected transmission and reception method in response to suchdesignation from the base station side (step S104).

[When Base Station is a Base Station that Effects Adaptive ArrayTransmission]

FIG. 4 represents the processing flow when base station 1000 effectsadaptive array transmission i. e. when base station 1000 effects signaltransmission having directivity with respect to adaptive array terminal2000.

Referring to FIG. 4, the terminal side informs the base station of areception allowable operation and transmission allowable operation (stepS200).

Base station 1000 selects and notifies the terminal of a transmissionand reception mode in accordance with the informed contents from theterminal 2000 side (step S202). For example, adaptive array receptioncan be designated for the reception mode, and adaptive arraytransmission can be designated for the transmission mode.

It is to be noted that, if base station 1000 effects adaptive arraytransmission, 1-antenna fixed reception can be designated for thereception mode, and any of maximum ratio composite transmission,directivity fixed transmission, reception level select transmissiondiversity, and 1-antenna fixed transmission can be selected.

Then, adaptive array terminal 2000 responds to the notification frombase station 1000 to select an adaptive array reception mode for thereception mode and an adaptive array transmission mode for thetransmission mode (step S204). At this stage, the reception weights aredirectly copied and used as the baseband transmission weights (stepS206) to suppress rapid change in the transmission weights at adaptivearray terminal 2000.

Alternatively, calculation weights can be calculated and used as thebaseband transmission weights based on the transmission response vectorestimated from the reception response vector information.

[When Base Station is SDMA Base Station]

FIG. 5 is a flow chart to describe a first transmission and receptionflow when base station 1000 is an SDMA base station. In other words, theflow chart corresponds to the case where base station 1000 conducts pathdivision multiple connection with a plurality of terminals by effectingadaptive array processing.

Referring to FIG. 5, the base station is informed of the receptionallowable operation and transmission allowable operation from theterminal side (step S300).

At base station 1000 side, designation of the reception and transmissionmodes is notified in accordance with the informed content from terminal2000 side (step S302). At this stage, an adaptive array reception modeis designated for the reception process whereas directivity fixedtransmission is designated for the transmission mode in accordance withbase station 1000 being an SDMA station. Alternatively, 1-antenna fixedtransmission can be selected.

Then, terminal 2000 designates the operation mode of transmission weightcalculator 2070 so as to effect reception by adaptive array receptionand transmission by directivity fixed transmission in accordance withthe notification from base station 1000 (step S304).

In response, at the terminal side, the amplitude of the basebandtransmission weight is fixed at equal gain, and the phase of thetransmission weight is fixed at a predetermined value (step S306).

As an arbitrary value of the value of the phase, the value can be fixedas set forth below. At adaptive array terminal 2000, such an arbitraryvalue of phase is recorded in memory 2100. Directivity fixedtransmission is effected using this phase value.

(ant 1, ant 2, ant 3, . . . , ant N)=(0°, 0°, 0°, . . . 0°)

(ant 1, ant 2, ant 3, . . . , ant N)=(0°, 90°, 0°, . . . 90°)

(ant 1, ant 2, ant 3, . . . , ant N)=(0°, 10°, 20°, . . . 360°)

Here, ant 1 represents the phase of antenna #1. In general, ant i (i=1,. . . N) represents the phase of antenna #i.

FIG. 6 is a flow chart of a second operation example when base station1000 is an SDMA base station.

In the example of FIG. 6, adaptive array terminal 2000 conductsdirectivity sub-fixed transmission in which the amplitude of thebaseband transmission weight is fixed at equal gain, and the phase ofthe transmission weight is gradually shifted according to the receptionresponse vector.

The gradually shifting process is effected as set forth below.

The weighted mean of the reception weight Wrx of the current frame andreception weight Wrx_old of the immediately preceding reception frame isobtained according to the equation set forth below. The phase of thetransmission weight is determined by extracting the phase value of thisweighted mean.Wrx =(1−α)Wrx_old/|Wrx_old|+αWrx/|Wrx|where 1<α<0, α is a predetermined value.

The above description is based on a configuration in which sudden changein transmission weight is suppressed by gradually altering the phaseaccording to the above-described procedure with the amplitude of thetransmission weight fixed.

It is to be noted that, if the transmission weight is to be determinedbased on the weighted mean between the information of an old frame andinformation of the current frame, a configuration can be employed inwhich the weight is calculated from a reception response vector that isthe weighted mean of, for example, the reception response vectorestimated at the time of determining the transmission weight of thecurrent frame and the reception response vector of an immediatelypreceding reception frame (or a reception response vector estimated byextrapolating at the time of transmission of the immediately precedingframe).

Alternatively, the weighted mean of a transmission weight Wtx calculatedin the current frame and a transmission weight Wtx_old of an immediatelypreceding transmission frame can be obtained by the equation set forthbelow, which is newly taken as the transmission weight /Wtx of thecurrent frame./Wtx=(1−α)Wtx_old+αWtx

FIG. 7 is a flow chart of a third operation example when base station1000 is an SDMA base station.

In comparison with the configuration of FIG. 6, the example of FIG. 7employs a configuration in which base station 1000 selects adaptivearray reception for reception and reception level select transmissiondiversity for transmission and notifies the same as the transmission andreception mode in accordance with the informed contents from terminal2000 side (step S502).

Accordingly, adaptive array terminal 2000 selects and sets the foregoingtransmission operation mode in accordance with the notification from thebase station (step S504). In a transmission mode, the antenna of highestreception level is selected for transmission (step S506).

SECOND EMBODIMENT

When directivity fixed or sub-fixed transmission is to be conducted atthe adaptive array terminal in the first embodiment, the value stored inmemory 2100 at the time of fabrication of adaptive array terminal 2000,for example, is employed for the transmission weight to be used.

In the second embodiment, a configuration is employed in which, when anadaptive array terminal 2200 of the second embodiment does not conductadaptive array transmission and reception in accordance with thecommunication status, a plurality of fixed values to be used for thetransmission weights are selectively collected and stored in advance inaccordance with the communication status corresponding to respectiveusages of relevant fixed values, and a base station 1002 of the secondembodiment designates selection and usage any of the plurality oftransmission weights.

FIG. 8 is a flow chart to describe the operation when terminal 2200 hastransmission weight select capability, and base station 1002 is an SDMAstation.

Referring to FIG. 8, the terminal 2200 side informs base station 1002 ofa reception allowable operation and transmission allowable operation(step 600).

In accordance with the informed contents from the terminal, the basestation designates, for example, an adaptive array reception mode forthe reception mode, and transmission weight select transmission for thetransmission mode (step 602).

In response, adaptive array terminal 2200 sets the aforementionedoperation mode of adaptive array reception and transmission weightselect transmission for the reception mode and transmission mode (step604).

Base station 1002 monitors the spatial correlation between receptionresponse vectors for respective signals from a plurality of terminals,and designates terminal 2200 to modify the transmission weight when thespatial correlation between upstream signals becomes high (step 606).

At the terminal 2200 side, signals are transmitted using thetransmission weight modified according to the specification from basestation 1002 (step 608).

FIG. 9 is a schematic block diagram to describe a configuration of anSDMA base station 1002 to specify a transmission and reception mode withrespect to adaptive array terminal 2200 having transmission weightselect capability.

The difference from the configuration of SDMA base station 1000 of FIG.1 lies in that terminal reception antenna designation adding unit IAP isreplaced with a transmission weight designation unit TWAP to addtransmission weight designation information to the baseband signal fortransmission based on an output from baseband unit BBP in accordancewith designation from control unit CNP, and a memory MP retaining thehistory of reception response vectors of a predetermined period of timefor respective terminals, and output/input the same from/to control unitCNP.

The remaining configuration is similar to the configuration of SDMA basestation 1000 of FIG. 1. The same corresponding elements have the samereference characters allotted, and description thereof will not berepeated.

FIG. 10 is a schematic block diagram to describe a configuration ofadaptive array terminal 2200 having transmission weight selectcapability.

The configuration of adaptive array terminal 2200 differs from that ofadaptive array terminal 2000 of FIG. 2 in that there are provided atransmission weight retain/select device 2210 receiving transmissionweight designation information from base station 1002, included in thesignal output from demodulation circuit 2040, for designating atransmission weight select operation, and a memory 2220 to store anorthogonal transmission weight table 2222 and a transmission weighttable 2224 for selection by transmission weight retain/select terminal2210. Further, transmission adaptive array 2090 multiplies the signal ofdemodulation circuit 2080 by transmission weights based on thetransmission weights from transmission weight retain/select device 2210,and provides the multiplied result to switch units 2020 and 2022.

The remaining features are similar to those of the configuration ofadaptive array terminal 2000 shown in FIG. 2. The same elements have thesame reference characters allotted, and description thereof will not berepeated.

In FIG. 10, reception level measurement unit 2010, error determinationcircuit 2050, base station type identify device 2060, transmissionweight calculator 2070 and memory 2100 shown in FIG. 2 are omitted. Inorder to allow adaptive array terminal 2200 to carry out an operationsimilar to that of adaptive array terminal 2000 of the first embodimentselectively in accordance with designation from base station 1002, aconfiguration in which such structural elements are provided in adaptivearray terminal 2200 can be employed.

FIGS. 11 and 12 are first and second flow charts, respectively, todescribe a table production process flow with respect to memory 2220 forthe transmission weight select capability of adaptive array terminal2200.

Referring to FIG. 11, upon initiation of the process (step S700), thevalues of variables i and j are set to the initial value of 0 (stepS702).

Transmission weight retain/select device 2210 of adaptive array terminal2200 reads out the transmission weight from the i-th table in memory2220 and sets the same as the transmission weight value (step S704). Itis assumed that max_i transmission weights are prestored in transmissionweight table 2224.

At the base station 1002 side, the reception response vector is measuredwhile receiving signals output from adaptive array terminal 2200 withthe selected transmission weight (step S706).

At base station 1002, determination is made whether it is the firstreception response vector from the start of table production (stepS708). When it is the first reception response vector, the value thereofis stored in memory MP (step S710).

When it is not the first reception response vector, base station 1002measures the spatial correlation between a reception response vectorwith respect to a signal from terminal 2200 and a reception responsevector from another terminal stored in memory MP (step S712).

When the spatial correlation is equal to or below a predeterminedthreshold value (step S714), transmission weight designation unit TWAPtransmits a transmission weight retain message to terminal 2200 (stepS716).

At terminal 2200, determination is made whether a weight retain messagefrom base station 1002 is received or not (step S718). When the messageis received, the value of variable j is incremented by 1 (step S720).The transmission weight at that time point is stored in the j-th tablein orthogonal transmission weight table 2222 (step S722).

Then, determination is made whether the value of variable i is largerthan a predetermined maximum value max_i (step S724). When not larger,the value of variable i is incremented by 1 (step S726), and the processreturns to step S704.

When the first reception response vector is stored in memory MP at stepS710, or when the spatial correlation is not equal to or below apredetermined value at step S714, or when the terminal has not receiveda weight retain message from the base station at step S718, the processproceeds to step S724.

When the value of variable i is equal to or above predetermined maximumvalue max_i at step S724, the process ends (step S730).

By such a process, the set of values of the orthogonal transmissionweight vectors that allows communication of relatively small spatialcorrelation with another terminal in the current communicationenvironment among the values retained in advance as transmission weightcan be stored in memory 2220.

When the communication environment changes, the set of orthogonaltransmission weight vector values can be updated by carrying out theprocess of steps S700–S730 again, as necessary.

FIG. 13 is a flow chart to describe a method of selecting a transmissionweight for communication between a terminal and a base station.

At the base station 1100 side, spatial multiplex communication betweenterminals 1 and 2 having a configuration similar to that of adaptivearray terminal 2200, for example, is set (step S800).

Designation is made from the base station 1002 side to terminal 1 to usethe first transmission weight in the orthogonal transmission weighttable as the transmission weight (step S802).

At adaptive array terminal 1, the orthogonal transmission weight is readout from the first table and set as the transmission weight (step S804).The number of the address where that transmission weight is set is X.

At the base station 1002 side, the spatial correlation between thereception response vector of terminal 1 and the reception responsevector of companion terminal 2 that is multiplexing with terminal 1 ismeasured (step S806).

Then, determination is made whether the spatial correlation is equal toor larger than a predetermined threshold value (step S808). When thespatial correlation is equal to or larger than the predeterminedthreshold value, designation is made from the base station 1002 side toset the transmission weight to a transmission weight other than that inthe Xth address (step S810).

Following this designation, determination is made whether transmissionhas ended or not (step S812). When transmission has not ended, theprocess returns to step S806.

In the case where transmission has ended, or when the spatialcorrelation is below the predetermined threshold value, thecommunication status is maintained.

The process of steps S805–S812 may be repeated during conversation, asnecessary.

As described with reference to FIG. 22, the same plurality of signalsarrive at SDMA base station 1002 from adaptive array terminal PS1 whensignals are transmitted and received between adaptive array terminal PS1and SDMA base station 1002. The reception signal X(t) at the SDMA basestation is represented as follows.X(t)=H ₁₁ W ₁ S ₁(t)+. . . +H _(1m) W ₂ S ₁(t)+H ₂ S ₂(t)X(t)=H ₁ S ₁(t)+H ₂ S ₂(t)H ₁ =H ₁₁ W ₁ +. . . +H _(1m) W ₂

Since the plurality of signals arriving from adaptive array terminal PS1are the same signals, the arriving direction corresponds to a compositevector of a plurality of signals.

FIG. 14 is a schematic diagram showing the status where such pluralityof arriving signals arrive at SDMA base station CS1. FIG. 15 is aschematic diagram to describe a reception response vector H₁ when suchplurality of arriving signals are represented as a composite vector.

FIG. 16 is a schematic diagram to describe change in the receptionresponse vector of signals from adaptive array terminal PS1 over time.

When the correlation value between response vector H₁ of adaptive arrayterminal PS1 and response vector H₂ of terminal PS2 is increased,degradation in communication quality will occur. Therefore, base stationCS1 designates terminal PS1 with the communication weight selectcapability to modify the transmission weight.

FIG. 17 is a schematic diagram to describe a reception response vectorfollowing designation of transmission weight modification.

In comparison with the case of FIG. 16, the uplink signal can be readilyseparated by reducing the correlation value between reception responsevector H_(1a) corresponding to terminal PS1 and response vector H₂ ofterminal PS2.

With regards to the transmission weight that is modified at terminal PS1in response to designation, a plurality of transmission weights may bestored in a fixed manner in orthogonal transmission weight table 2222,in addition to the configuration of searching for and storing in thememory a weight of high orthogonality while conducting communicationwith the base station. Alternatively, a configuration in which weightsof high orthogonality are set in ranks while conducting communicationwith base station CS1 can be employed.

The first and second embodiments set forth above are based mainly oncalculation of a transmission weight.

In the calculation of a reception weight at the adaptive array terminaldescribed in the first and second embodiments, the time required forcalculating a reception weight can be reduced by dynamically modifyingthe setting of the initial value in accordance with modification of thetransmission weight.

For example, when the reception weight is to be updated by the leastmean square error algorithm (LMS algorithm) based on the steepestdescent method, the time for convergence of the transmission weight canbe reduced by taking the initial value of the reception weight as thetransmission weight.

Alternatively, when the reception weight is to be modified by therecursive least square method (RLS algorithm), the time for convergenceof the reception weight can be reduced by setting the initial value ofthe reception weight as the transmission weight, or by setting a valuecalculated from the response vector at the time of transmission for theinitial value of the reception correlation matrix.

These LMS algorithm and RLS algorithm are disclosed in theaforementioned Document 1.

As described above, the invention of the present application allowsimprovement in communication quality as compared to a conventionaladaptive array terminal by applying restriction so as to change thetransmission weight gradually when in communication with a base stationthat communicates under the spatial multiple access system.

Furthermore, the communication quality can be improved when thetransmission method is adaptively switched in an area where there is amixture of base stations communicating under the spatial multiple accesssystem and another system.

INDUSTRIAL APPLICABILITY

The invention of the present application is advantageous in that thecommunication quality can be improved by applying restriction so as toset the modification of the transmission weight to be altered graduallywhen an adaptive array terminal communicates with a base station of aspatial multiple access system.

1. A radio terminal apparatus comprising: an array antenna including aplurality of antennas (#ANT 1, #ANT 2), a reception signal processingunit extracting a reception signal from a base station by multiplyingsignals from respective said antennas of said array antenna byrespective reception weights, a transmission signal processing unitapplying to respective said antennas of said array antenna a pluralityof signals generated by multiplying a transmission signal bytransmission weights to form transmission directivity, and transmissionweight generation means for adaptively switching between a mode ofcalculating transmission weights forming transmission directivitytowards said base station and a mode of calculating said transmissionweights added with a specified constraint, in accordance withdesignation in said reception signal, to generate said transmissionweights.
 2. The radio terminal apparatus according to claim 1, whereinsaid transmission weight generation means provides, when said receptionsignal processing unit multiplies a signal from said base station byreception weights having reception directivity, said reception weightsas said transmission weights to said transmission signal processingunit, in accordance with designation from said base station.
 3. Theradio terminal apparatus according to claim 1, wherein said transmissionweight generation means generates, when said reception signal processingunit multiplies a signal from said base station by reception weightshaving reception directivity, said transmission weights based on atransmission response vector estimated from a reception response vector,in accordance with designation from said base station.
 4. The radioterminal apparatus according to claim 1, wherein said transmissionweight generation means sets said transmission weight with a fixedamplitude and phase when said reception signal processing unitmultiplies a signal from said base station by reception weights havingreception directivity, in accordance with designation from said basestation.
 5. The radio terminal apparatus according to claim 1, whereinsaid transmission weight generation means carries out a process ofsetting a fixed value of amplitude of said transmission weight, andgradually shifting a phase of said transmission weight according to apredetermined sequence when said reception signal processing unitmultiplies a signal from said base station by reception weights havingreception directivity, in accordance with designation from said basestation.
 6. The radio terminal apparatus according to claim 5, wherein asignal transferred between said base station and said radio terminalapparatus is divided into a plurality of frames, said transmissionweight generation means calculates said phase of said transmissionweight by a weighted mean of said reception weights in past and currentframes.
 7. The radio terminal apparatus according to claim 1, wherein asignal transferred between said base station and said radio terminalapparatus is divided into a plurality of frames, said transmissionweight generation means calculates said transmission weight based on aweighted mean of reception response vectors in past and current frameswhen said reception signal processing unit multiplies a signal from saidbase station by reception weights having reception directivity, inaccordance with designation from said base station.
 8. The radioterminal apparatus according to claim 1, further comprising receptionlevel detection means for detecting a reception level of each of saidantennas, wherein said transmission weight generation means generatessaid transmission weights so as to select an antenna of the highestreception level.
 9. The radio terminal apparatus according to claim 1,wherein a signal transferred between said base station and said radioterminal apparatus is divided into a plurality of frames, saidtransmission weight generation means takes a weighted mean oftransmission weights calculated in past and current frames newly as atransmission weight of the current frame when said reception signalprocessing unit multiplies a signal from said base station by areception weight having reception directivity, in accordance withdesignation from said base station.
 10. The radio terminal apparatusaccording to claim 1, further comprising storage means for storing inadvance a set of transmission weights that increases orthogonality ofreception response vectors at said base station, wherein saidtransmission weight generation means selects and provides to saidtransmission signal processing unit said transmission weight stored insaid storage means, in accordance with designation from said basestation.
 11. A transmission directivity control method of a radioterminal apparatus including an array antenna having a plurality ofantennas (#ANT 1, #ANT 2) and for separating and extracting a receptionsignal from a base station by multiplying signals from respective saidantennas of said array antenna by respective reception weights, saidmethod comprising the steps of: adaptively switching between a mode ofcalculating transmission weights forming transmission directivitytowards said base station and a mode of calculating said transmissionweights added with a specified constraint, in accordance withdesignation in said reception signal, to generate said transmissionweights, and providing to respective said antennas of said array antennaa plurality of signals generated by multiplying a transmission signal bysaid transmission weights to form said transmission directivity.
 12. Thetransmission directivity control method according to claim 11, whereinsaid step of generating transmission weights includes the step of, whena signal from said base station is multiplied by reception weightshaving reception directivity, taking said reception weights as saidtransmission weights, in accordance with designation from said basestation.
 13. The transmission directivity control method according toclaim 11, wherein said step of generating transmission weights includesthe step of generating, when a signal from said base station ismultiplied by reception weights having reception directivity, saidtransmission weights based on a transmission response vector estimatedfrom a reception response vector, in accordance with designation fromsaid base station.
 14. The transmission directivity control methodaccording to claim 11, wherein said step of generating transmissionweights includes the step of setting said transmission weight with afixed amplitude and phase when a signal from said base station ismultiplied by reception weights having reception directivity, inaccordance with designation from said base station.
 15. The transmissiondirectivity control method according to claim 11, wherein said step ofgenerating transmission weights includes the step of, when saidreception signal processing unit multiplies a signal from said basestation by reception weights having reception directivity, carrying outa process of setting a fixed value of amplitude of said transmissionweight, and gradually shifting a phase of said transmission weightaccording to a predetermined sequence, in accordance with designationfrom said base station.
 16. The transmission directivity control methodaccording to claim 11, wherein a signal transferred between said basestation and said radio terminal apparatus is divided into a plurality offrames, said step of generating transmission weights includes the stepof calculating a phase of said transmission weight based on a weighedmean of said reception weights in past and current frames.
 17. Thetransmission directivity control method according to claim 11, wherein asignal transferred between said base station and said radio terminalapparatus is divided into a plurality of frames, said step of generatingtransmission weights includes the step of calculating said transmissionweight based on a weighted mean of reception response vectors in pastand current frames when a signal from said base station is multiplied byreception weights having reception directivity, in accordance withdesignation from said base station.
 18. The transmission directivitycontrol method according to claim 11, further comprising the step ofdetecting a reception level of each of said antennas, wherein said stepof generating transmission weights includes the step of generating saidtransmission weights so as to select an antenna of highest receptionlevel.
 19. The transmission directivity control method according toclaim 11, wherein a signal transferred between said base station andsaid radio terminal apparatus is divided into a plurality of frames,said step of generating transmission weights includes the step of takinga weighted mean of transmission weights calculated in past and currentframes newly as a transmission weight of the current frame when a signalfrom said base station is multiplied by reception weights havingreception directivity, in accordance with designation from said basestation.
 20. The transmission directivity control method according toclaim 11, further comprising the step of storing in advance a set oftransmission weights that increases orthogonality of reception responsevectors at said base station, wherein said step of generatingtransmission weights includes the step of selecting said transmissionweight stored in advance in accordance with designation from said basestation.
 21. A transmission directivity control program of a radioterminal apparatus including an array antenna having a plurality ofantennas (#ANT 1, #ANT 2) and for separating and extracting a receptionsignal from a base station by multiplying signals from respective saidantennas of said array antenna by respective reception weights, saidprogram causing a computer to execute the steps of: adaptively switchingbetween a mode of calculating transmission weights forming transmissiondirectivity towards said base station and a mode of calculating saidtransmission weights added with a specified constraint, in accordancewith designation in said reception signal, to generate said transmissionweights, and providing to respective said antennas of said array antennaa plurality of signals generated by multiplying a transmission signal bysaid transmission weights to form said transmission directivity.
 22. Thetransmission directivity control program according to claim 21, whereinsaid step of generating transmission weights includes the step of, whena signal from said base station is multiplied by reception weightshaving reception directivity, taking said reception weights as saidtransmission weights, in accordance with designation from said basestation.
 23. The transmission directivity control program according toclaim 21, wherein said step of generating transmission weights includesthe step of generating, when a signal from said base station ismultiplied by reception weights having reception directivity, saidtransmission weights based on a transmission response vector estimatedfrom a reception response vector, in accordance with designation fromsaid base station.
 24. The transmission directivity control programaccording to claim 21, wherein said step of generating transmissionweights includes the step of setting said transmission weight with afixed amplitude and phase when a signal from said base station ismultiplied by reception weights having reception directivity, inaccordance with designation from said base station.
 25. The transmissiondirectivity control program according to claim 21, wherein said step ofgenerating transmission weights includes the step of, when saidreception signal processing unit multiplies a signal from said basestation by reception weights having reception directivity, carrying outa process of setting a fixed value of amplitude of said transmissionweight, and gradually shifting a phase of said transmission weightaccording to a predetermined sequence, in accordance with designationfrom said base station.
 26. The transmission directivity control programaccording to claim 21, wherein a signal transferred between said basestation and said radio terminal apparatus is divided into a plurality offrames, said step of generating transmission weights includes the stepof calculating said phase of said transmission weight based on a weighedmean of said reception weights in past and current frames.
 27. Thetransmission directivity control program according to claim 21, whereina signal transferred between said base station and said radio terminalapparatus is divided into a plurality of frames, said step of generatingtransmission weights includes the step of calculating said transmissionweight based on a weighted mean of reception response vectors in pastand current frames, when a signal from said base station is multipliedby reception weights having reception directivity, in accordance withdesignation from said base station.
 28. The transmission directivitycontrol program according to claim 21, further comprising the step ofdetecting a reception level of each of said antennas, wherein said stepof generating transmission weights includes the step of generating saidtransmission weights so as to select an antenna of highest receptionlevel.
 29. The transmission directivity control program according toclaim 21, wherein a signal transferred between said base station andsaid radio terminal apparatus is divided into a plurality of frames,said step of generating transmission weights includes the step of takinga weighted mean of transmission weights calculated in past and currentframes newly as a transmission weight of the current frame when a signalfrom said base station is multiplied by reception weights havingreception directivity, in accordance with designation from said basestation.
 30. The transmission directivity control program according toclaim 21, further comprising the step of storing in advance a set oftransmission weights that increases orthogonality of reception responsevectors at said base station, wherein said step of generatingtransmission weights includes the step of selecting said transmissionweight stored in advance in accordance with designation from said basestation.